PRESSURE EFFECTS ON THE PHASE-BEHAVIOR OF A PROPYLENE WATER SURFACTANT MIXTURE

The phase behavior of the propylene/water/Tergitol 7 surfactant ternary mixture has been examined as a function of pressure at 25.5-degrees-C. Unlike conventional liquid alkane based systems, a three-phase region is obtained in the absence of added electrolyte. This is likely due to a higher upper critical solution temperature for the propylene/Tergitol 7 binary mixture, in comparison to that for mixtures of various anionic surfactants and liquid alkanes. The effect of increasing pressure is similar to the effect of decreasing temperature or increasing electrolyte concentration, according to the Kahlweit phenomenological model for amphiphile/water/oil phase behavior (as well as models describing effects on interfacial curvature, such as the R ratio). The conductivities of the nominally propylene-continuous upper phases in the systems examined are high enough to suggest electrical percolation, implying the presence of significant volume fractions of micelles in these phases.